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Topics - Rockhorst

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1
Open Discussion / Looking for ideas on a troubled Marshall Valvestate
« on: June 20, 2020, 11:23:31 AM »
*note: schematic attached at the bottom*

A friend of mine came by with his Marshall 8280 Valvestate Bi-Chorus. It has a clean/crunch and a OD1/OD2 channel. When OD2 is selected, playing chunky riffs through high output pickups (passive or active) on the lowest string, especially with palm mutes in there, the amp clamps down the signal. Trying to describe it in words I would say it sounds like your signal is 'sucked' away. It's like a really aggressive compressor that sucks away tone, volume, crunch and only releases when you let the guitar ring out again. The amp was in storage for a long time but my friend does believe that it didn't do this in the past. What I've tried so far:

- replace 12AX7
- replace power filtering caps
- replace the caps around the 12AX7

I then audio probed through the preamp circuit and found that the problem is really early on in the circuit, before the tone controls and also before the tube, although it gets more pronounced/amplified by the tube stage. Something around the dual opamp gain stage is causing problems. My friend also has the 40W version of this amp and he claims that it slays the 2x100W version. I've put the partial schematics of the input stages side by side and attached it. Note that the dual opamp has an internal switch: only one half is active at every time (neat trick to switch channels by the way, could be useful for projects!). The 8280 has a discrete mosfet input stage before the opamp. The 40W version uses a TL072 instead and according to the schematic has a 720Hz roll off.

My working hypothesis right now is that there's too much bass going into the amp and that I may be able to tame that down by lowering C2.
That said, I'd like some alternative suggestions if there's anything on offer.


2
Open Discussion / Looking for EHX Qtron+ SPDT switch
« on: May 05, 2020, 11:01:14 AM »
I'm looking for a bulky, square SPDT switch used in the EHX Qtron+. It's the boost switch on the unit that's gone faulty. I reached out to EHX but haven't hear back.

Picture attached, it's the switch on the far right.

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Open Discussion / Anybody playing Star Wars Battlefront 2?
« on: May 27, 2019, 02:58:06 AM »
So I decided I'd like to play a game again and being a Star Wars nerd I decided to jump into Battlefront 2, two years after release. It's a bit of a grind to get the abilities up to par with players that have been there for a long time but I find it greatly enjoyable (and way to much of a distraction). The game is still regularly updated. I was wondering if there's anybody here that plays it, so I can be on the lookout for you :)

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Open Discussion / (the impact of) dermatitis and eczema
« on: April 10, 2019, 04:07:08 PM »
I've been putting this write up off for a while. On the other hand I've seen others share very personal stuff here and I think it might be therapeutic...IRL I notice how much talking about it improves at least my mental state of being. So here it goes.

I was born with eczema. Lots of people have it in some form or the other. Standard treatment is steroid cremes. Some people out grow the disease. With me it's been getting steadily worse over time. The cause (at least for me) is very clearly auto-immune. My body basically attacks itself, specifically the skin. It becomes itchy, I sratch, bacteria get in and infect the place, regularly resulting in quite enormous inflamed bumps in random places. This ranges from a few centimeters to half of my face. When it's in the neck, it becomes hard to turn my head. Once it was actually pressing on my wind pipe. Stuff like that. The skin is very dry at times, red and raised, warm and itchy.

Last summer was very hot in The Netherlands. Basically I spent 4 weeks in bed, because anything else was unbearable. When I returned to work (teaching) in September I was not well rested and had not had my mental 'reset'. I had also lost my faith in dermatologists. So as the symptoms kept getting worse and worse, I did not go see the dermatologist. They'll just give me another creme, it'll work for a bit and then everything is back to being F'ed up, so why bother. I tried to ignore the urge to scratch but as soon as I got home from work I'd lose control. I'd regularly scratch my face raw in a towel for instance. The mechanism is this: for a brief moment you feel release and the pain from the scratch drowns out the itch. 10 seceonds after you stop you start to feel very sorry though, because of the damage done to the skin that will keep the cycle going. A few times a day I feel myself heating up from the inside and I go off, unless there's somebody else around...social pressure helps.

Something else...for some years I've rationalized the state of my skin: yes it feels nasty, there's some redness but in all it's not that bad. That myth shattered a bit over the year. In one incident some students sent anonymous e-mails to teachers with weird remarks. I got some about the skin. In another incident, where I crossed the street, some random dude in a car yelled at me and basically mocked my skin. Stuff like that has been happening, also adding to the psychological stress.

My physician suggested I use prednison when things get really rough. About half a week on a medium dose usually was enough to get back to a doable situation. I've done that about 7 times in two years. Starting december 2018 I started noticing weird stuff with my eyes. Over the past 3 months I've become very sensitive to light and I can barely read. Turns out I've developed cataracts in both eyes...I'm 36. Visus in the left eye is down to 20%, right is 60%. It's a known side effect of the prednison, but this is extremely fast and progressive. So two operations are coming. It's a pretty standard procedure but the fact that my skin disease has indirectly damaged my previously better than 20/20 vision is a real psychological hurdle.

Two weeks ago I finally got a appointment with the dermatologist again. Basically, there was not a healthy inch of skin left, something had to be done. I'm now on an even more aggressive type of steroid creme (dermovate). Within 12 hours of first applying it the lights went back on in my head. The creme suppresses the immune system, blocking the reaction and thus stopping all the signals that it produces from clogging up my brain. For the first time I really realized how much brain power was being occupied by coping with the dermatitis. I've been very lucid for two weeks now, but was numb for over 6 months. No other way to describe it.

I hope I can start being creative again real soon. Because of the cataracts I basically see jack shit during the day without wearing two sunglasses at the same time. Night time is much better. Road cycling and fine soldering will have to wait until after the surgery. I've started UV-B therapy for the skin, to see what the effects are and I'm going to discuss long term plans with the dermatologist soon. Three years ago, she mentioned that research was expected to find the cause of chronic eczema in 10 to 30 years. Two weeks ago, the said 1 to 3 years. There's new treatments but they are quite expensive so access to them is restriced.

Sorry for the long post, hope it's not a bother. Long story short: the eczema sucks, but I've come to realize that it also comes with a psychological component that, for me at the moment, is equally alarming.

5
Open Discussion / A few questions about 'gold caps'
« on: March 25, 2019, 02:03:40 AM »
I bought some gold caps for a physics project (I'll share it sometime soon). These have a very small form factor, usually a disc of about 1 cm across, but a ludicrously high capacitance, like the 200 mF (0.2 F) I was looking for. They can only take up to 5.5 V though. Their main application is in motherboards and the like.

Some initial testing shows that these caps do not charge/discharge following a nice exponential. Rather, there is a fast initial step, followed by a slower exponential rise/decay. Curves match this technical guide.

I have some questions, hoping someone here is more savvy on these components than me:

- is there a way to force rise/decay to conform better with a single exponential function instead of two joined together? I kinda need that for the experiment to make sense for students.

- any other suggestions where I may find a capacitor in the range of 10 mF (0.01F) and up withouth it being quite bulky?

- these caps are quite affordable (about $1 a piece), any use for them in pedals? I'm thinking maybe capacitors for digital circuits, either high end or in the power supply of a PT2399 circuit?

6
Open Discussion / Looking for help with an actual vintage EHX Memory Man
« on: February 10, 2019, 05:52:11 PM »
note: pictures of the unit attached.

Someone sent me an early EHX Memory Man hoping I can repair it. I'm a bit apprehensive to start working on it, so I hope someone with experience with these units can help me out a bit. It looks like there have been some modifications over the years, the transformer is dead and there's a loose wire coming from the boost switch. No clue if the delay chips are still good. Still looking for a verified schematic for this particular unit.

On the EHX forum I found that a replacement transformer for the DMM is the F-115X which Mouser carries. I'm going to compare some specs, but I expect it will work with the MM as well. I have a EHX 24V center positive wall wart, was wondering if I can use this to test the unit before buying the transformer.

Any other suggestions for testing the unit are very welcome.

7
Tech Help - Projects Page / Harbinger One - Rate LED not flashing
« on: December 22, 2018, 10:21:20 AM »
Two questions:

1) what's the benefit of the buffered rate LED circuit in the 2015 Harbinger compared to the old version? Is it to prevent ticking?

2) I subbed a BC560C for the 2N5087 in the rate LED circuit and the LED doesn't flash now. It does sometimes, but usually is just permanently on. Maybe I see a very faint flickering. Could this be due to the substitution? I looks to me like the 1uF cap may be charging up to quickly and the potential not going down anymore. Maybe subbing a smaller cap will fix it, but maybe there's other ideas?

Other than this, the build is working fine by the way :)

8
Open Discussion / Understanding Ring Modulators (Physics article)
« on: November 16, 2018, 02:04:24 AM »
I'm toying with the idea of making some pedal/effects based education kits to use in my physics class room. It's potentially a great way to get kids more involved in the subject of electricity and electrical systems (as VFE has also clearly demonstrated). Anyway, this week I received the latest issue of The Physics Teacher and one of this month's freely readable articles discusses ring modulators and specifically the Moogerfooger MF102. How cool is that :) Caveat: it doesn't discuss the actual electronics, but goes into how ring mods shift frequencies around.

Read it here
(there's also a downloadable PDF available on the same page)

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Open Discussion / Desoldering station suggestions anyone?
« on: October 25, 2018, 05:01:16 PM »
I'm getting more and more tired of using braid and a sucker. I think my (repair) work would really benefit from a dedicated desoldering station. I'm guessing the heat stress on components would also be a lot less. These things seems to be quite expensive though (much more expensive than a reasonable soldering iron). Any suggestions, cheap (but good) stuff or expensive? Preferably something that is easy to get in Europe. What should I look out for? Features, things to consider for trough hole vs smd etc. I also use both leaded and lead free stuff. I have two separate irons for that, does one need to different suckers?

10
Open Discussion / Question for EMG connaisseurs
« on: October 09, 2018, 01:47:31 AM »
I've got a few Jackson Rhoads guitars with EMGs. One has just a single EMG 81 in the bridge and when I'm in a Swedish metal mood that works out just fine. I've also tried a spare 85 I had around in the bridge position (heard some good stuff about that) but didn't like that. Sometimes I do want to use the neck pickup but I've found that I also don't really like the 85 in that position. It's hard to describe. It's not actually muddy, but it feels like it. Sluggish, not enough attack. Something like that.

So the question is: anyone else here
1) like the 81
2) dislike the 85
3) got a good alternative from the EMG pickup line? (not looking for a complete wiring overhaul).

11
Open Discussion / NVD - or - that's what friends are for
« on: July 12, 2018, 03:51:06 AM »
So Björn, my Dutch-Swedish brother in metal, recorded a record last year with his band Graceless called Shadowlands. It's OSDM, so not too complicated, straight for the kill, zombie themed death metal. They got very favourable reviews from various magazines (average 8 out of 10). Anyway, I've been designing a distortion pedal for him since August (the Saturn V) for which the (for now) final version just got released. We've been tweaking his live rig over the past few months in the rehearsal space and it's a lot of fun seeing his live sound come together. It's the part I've always enjoyed the most: helping people sculpt their sound.

NVD: new vinyl day. Their record just got a vinyl release, see attached picture. Bottom right corner. How flippin' cool is that? Humbled and stoked at the same time. So the least I can do is give him a plug here as well, see above (not a lot of metal people here I believe, but hey).

12
Build Reports / Harbinger 2, sort of ;)
« on: February 26, 2018, 10:54:40 AM »
Sorry for the tongue-in-cheeck title Brian ;)

A client asked me to install his Dry Bell Vibe Machine into a Shin-Ei wah enclosure. The original pedal has a ludicrous amount of options (google the options manual to go insane). Now it also has that vintage mojo ;)


13
Open Discussion / NWD
« on: January 05, 2018, 08:34:58 AM »
New Workplace Day! There's a baby boy coming sometime in the middle of March, so we had to rethink the rooms in our house a bit. We decided to move the soldering room to the other side of the upstairs hall. Once we had installed a desk and stuff like that, it took the time between Christmas and New Year's to move everything.Why? Cuz I'm not the tidiest person in the universe. Luckily, my girlfriend loves sorting stuff. I ordered a few extra parts cabinets, explained the difference between resistor, capacitor and IC markings and we set to work. I've never before been this organized. Lighting is not ideal, but below is a guided tour in photos:

The new room is smaller and has a sloping ceiling, but actually, I now feel it's the better room because it has no weird corners and such like the other one. Behind those white panels at the far end, there's secret storage space.


On the left, there's storage (boxes boxes, parts parts, pedals pedals) and a place to populate PCBs


As I said: never been this organized before


Pedals and a DIY 18W combo amp hiding under the cover


On the far end on the right is a space to assemble pedals or take them apart, with appropriate tools nearby and containers to stash the parts so they don't get lost while working on the pedal.


Also shown here is my little test setup: a looper with She Sells Sanctuary played into it, a sort of break out box with aligator clips to hook up circuits, and a small practice amp. Behind that is a power supply. Simple, but this makes repair jobs and testing so much easier.


And finally, this is where the soldering should happen. I bought a second soldering iron. Instead of switching tips (and waiting for them to cool down) I now can just switch soldering irons when changing from leaded to lead free. I've switched to lead free for new projects permanently. It's actually working out pretty well. The parts bins contain switches and pots.

14
I've been assembling a 6u rack unit for 80s metal and hard rock toonz. The JMP-1 I bought second hand has some problems. It sometimes loses about 20dB of signal level. Not fully intermittent, but very annoying and unpredictable. So far I've concluded that the input jack could use a replacement (ordered it, it's an odd ball part, mirrored from the standard switched jacks). The tubes inside are still the original Marshall ones, so I'll replace those as well. That may solve all my problems. However, there's also a 3.2V Lion battery inside that maintains the presets in the memory and will need to be changed periodically. Here's the thing: I can't get the circuit board out (at least, not in one piece, I suspect) and can't find a service manual, step-by-step guide or whatever.

So, any JMP-1 users here with some experience with taking the unit apart and modding it? There's really very little on the net to be found.

15
Open Discussion / Ibanez WH10 tone suck
« on: October 31, 2017, 02:51:01 AM »
I'd like some input on this one from here if possible. I posted it over at DIYSB as well, seems to best fit the Open Discussion part of the forum. Take a look at this schematic if you can. Any clues why this sucks massive high end and volume in bypass? The pedal doesn't suck tone with another buffer in front of it and I'd like to understand why. I've removed those 2n2 caps and tried raising the input impedance by bumping the 510k to a 1M, but with little effect. My next bet would be to remove/or lower the 220R series resistors at the input, but I doubt that will do much. My thoughts are drifting more towards the input stage not being able to drive both the clean signal and the wah signal. It's being split in two/three and later mixed together when the effect is on.

The fix, in any case, is easy: put another buffer in the enclosure, either at the input or between clean and wah signal to separate the two. I'd just like to understand it a little bit better.

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